The present invention relates generally to vacuum operated circuit breaker apparatus for replacing air magnetic circuit breaker assemblies. More particularly, the present invention deals with replacement vacuum operated circuit breaker apparatus for air-magnetic circuit breaker assemblies when retrofitting the existing air-magnetic breaker with conventional vacuum operated components is impossible or impractical.
Generally, older voltage distribution systems incorporate switchgear built around air-magnetic (referred to hereinafter as "A-M") circuit breakers. Maintenance on these older distribution systems has become increasingly expensive and time consuming as the systems age. The expense and increased maintenance is largely attributable to the inherent design and construction of all A-M breakers which generally require substantial numbers of new parts to keep the breakers operational as the breakers age.
Metal clad A-M breakers of these older systems specifically designed to be used in 5 kilovolt (KV) switchgear, were manufactured by Allis Chalmers during the late 1940's and early 1950's. These A-M breakers were designed around the criteria of 600, 1200 and 2000 ampere continuous current with various interrupting capabilities ranging from 50 to 250 million volt-amperes (MVA). The Allis Chalmers A-M circuit breaker is designed to be installed horizontally into a cubicle and then racked vertically into an operating position by an elevator. During the middle to late 1950's, Allis Chalmers discontinued manufacturing these A-M circuit breakers and no A-M circuit breakers have been built since that time which are compatible with the vertical lift switchgear. Accordingly, replacement parts for such vertical lift A-M circuit breakers have become increasingly scarce and expensive.
Over the last decade, vacuum operated circuit breakers have generally replaced A-M breakers in new switchgear installations due to the substantial benefits provided. It is well known to those skilled in the art that vacuum circuit breakers are at least ten times more reliable than their A-M counterparts. Furthermore, vacuum technology permits a substantial reduction in circuit breaker size and weight while allowing the breaker to interrupt in two-to-three cycles versus the eight or more cycles required by A-M breakers. Vacuum operated breakers are also far simpler in construction and provide lowered maintenance requirements over the life of the voltage distribution system.
The superior reliability and lower maintenance costs of vacuum operated circuit breakers combined with the scarcity and expense of A-M replacement parts have made it cost effective and desirable to replace A-M breakers with vacuum operated breakers. The expense of installing all new switchgear can be avoided by retrofitting the A-M circuit breakers with vacuum operated components. A-M breaker parts common to both the A-M and vacuum operated circuit breakers are retained while all other parts are replaced by vacuum components.
The A-M circuit breakers are typically housed together in a assembly contained within a frame. For a retrofit to be practical, both the individual A-M breaker and the assembly frame must have a design which permits the installation of vacuum operated components without substantial modifications to the breaker or the frame. Retrofitting the A-M circuit breakers with vacuum operated components has been determined to be less costly than replacement of the entire switchgear. A further advantage is that the older frame and electrical contacts are already configured to fit into the switchgear cubicle. A vacuum retrofitted breaker assembly thus fits easily into the original cubicle. Retrofits for A-M breakers are sometimes available from the original or other manufacturers. However, the configuration of some A-M circuit breakers, such as the Allis Chalmers 5 KV series, make it impossible or impractical to retrofit the individual breakers with vacuum components. Attempts to retrofit the Allis Chalmers A-M breaker have been unsuccessful and when retrofitted unable to provide the required protection, current handling capacity or sensitivity required in the 5 KV power class.
When a retrofit for the A-M breaker is impractical, the only alternative apart from replacing the switchgear is to replace the entire A-M breaker assembly with a vacuum operated breaker assembly. One major drawback is however that the frame and power buses of the replacement vacuum operated breaker assembly must often be configured differently than in the original A-M breaker assembly. The various different configurations require that the switchgear cubicle also be modified in each case so that the replacement assembly can be accommodated for proper operation. Any cubicle modifications add complexity and expense to the retrofit costs in addition to increasing the downtime of the switchgear. Also, as in the case with individual A-M breaker retrofits, it may be impossible or extremely expensive to modify certain cubicles to accept conventional replacement vacuum operated breaker assemblies.
Accordingly, it is a general aim of the present invention to provide a vacuum operated circuit breaker assembly for replacing A-M circuit breaker assemblies in switchgear when retrofitting the individual A-M circuit breakers with vacuum operated components is impractical or impossible.
It is a further aim of the present invention to provide a replacement vacuum operated circuit breaker assembly that may be installed in switchgear cubicles without expensive and time consuming modifications of the cubicle.